Nitrogen Doping of Hexagonal and Cubic Ge2Sb2Te5 Nanocrystals: An Ab Initio Study

The effect of nitrogen doping on the structural, electronic and optical properties of hexagonal and cubic Ge2Sb2Te5 (GST) has been investigated from first principles. The nitrogen content was set to 10 at.% and 25 at.%, in which it was found that the hexagonal phase becomes more stable, whereas the cubic phase becomes more unstable with increasing nitrogen content. A difference in optical reflectivity of about 8% was calculated for pure hexagonal and cubic phases. Pure GST was found to possess a higher reflectivity contrast in the infrared spectral range, whereas doped GST had a higher reflectivity contrast, which increased with rising nitrogen content, in the visible and ultraviolet spectral range. The optical conductivity was found to fall with increasing nitrogen content, in agreement with experiment and other theoretical studies.